This is a request for extension of the Training Program in Environmental Health Statistics at the Harvard School of Public Health. The Program prepares predoctoral students and postdoctoral fellows for research careers in the application of biostatistics to environmental health. The Program will be administered through the Department of Biostatistics, with active participation by faculty members from the Kresge Center for Environmental Health and the Department of Epidemiology, also located at the Harvard School of Public Health. Trainees will receive high-quality instruction in basic biostatistical models, such as probability, statistical inference, computing and data analysis. The Program will also provide training in specialized topics of particular relevance for environmental applications, such as longitudinal analysis, methods for the analysis of categorical data, missing data techniques, and statistical methods relevant to environmental exposure assessment, such as measurement error models. Training will also be provided through applied course work in environmental health and a regular seminar series called "Statistics and the Environment", where faculty, students, and fellows present their own environmental health-related research. An important focus of training will be the opportunity to collaborate with faculty members on biostatistical research as it applies to environmental health. All trainees will participate in Harvard's program on scientific integrity in the conduct of research. Since its inception in 1982, this Training Program has emphasized strong links to the environmental sciences. In recent years, Program trainers have placed particular importance on the recruitment of students from underrepresented minority groups. The focus on interdisciplinary training at the Harvard School of Public Health, as well as its talented and diverse student body and faculty, makes it ideally suited for a Training Program in environmental statistics.